Interchannel Facies Research Articles

Stratigraphy and paleogeographic environments for the forming the Carpian Series (Stryi and Opir River basins, Ukrainian Carpathians)

Results of studying the Carpian Series – a component of the thick Lower Cretaceous-Miocene flysch of the Outer (Flysch) Carpathians are presented in the article. Sediments of the Carpian Series (Middle Paleocene – Eocene) were studied in the Skole Beskids in the basin of the middle and lower reaches of the river Opir in the area of conducting geological and geographical educational practices of students of Ukrainian universities. Using the method of sedimentological analysis, it was found that the investigated sediments are the product of the activity of gravitational flows (mainly turbidites, as well as grainites, debrites), bottom currents and background hemipelagic sedimentation. These sediments are compared with the facies of deep-marine fans placed on the continental slope and its foot. Medium- and coarse-grained turbidites and grainites (Yamna and Vyhoda formations) correspond to the submarine valley-channel facies. Fine- and medium-grained turbidites and hemipelagites (Manyava and Bystrytsa formations) belong to the inter-channel facies. The composition of the clastic material (green and red phyllites) suggests, that the sediments were drifted from the Eurasian continental margin into the deep-marine fan (fans?). Applying the micropaleontological method, it was established that the Paleocene-Eocene background red and green clay hemipelagites are enriched in buried in situ benthic foraminifera (deep-water agglutinated foraminifera: DWAF), which indicate lower bathyal – abyssal depths of flysch accumulation below a calcite compensation depth (CCD). Late Eocene calcareous lithofacies of the Popiele Formation contain a mixed foraminifera assemblage formed as a result of mud and debris flows. Shallow-water fauna and “exotic” debris (including the red and green phyllites) were transferred from the shelf area to the deep basin. The Latest Eocene hemipelagic clay-carbonate sediments of the Sheshorian horizon contain the foraminiferal assemblage with plankton dominance, which indicates a general shallowing of the paleobasin (middle-upper bathyal conditions above a calcite compensation depth) at the end of the Carpian time. Key words: stratigraphy, paleogeography, Ukrainian Outer Carpathians, Paleocene-Eocene flysch, turbidites, foraminifera.

Turbidite reservoirs of the Sele Formation, Central North Sea: geological challenges for improving production

Turbidite reservoirs of the Sele Formation in the Central North Sea produce from fields such as Forties, Nelson, Montrose–Arbroath, Scoter, Pierce, the Gannet cluster, Guillemot A, Mirren and are under appraisal/development in fields such as Merganser, Phyllis, Starling and Blane. These reservoirs form part of the ‘Forties’ submarine fan system that was sourced from feeder channels in the northwest and west. Blanket 3D seismic coverage tied to wells shows that nearer their updip sources the turbidites are thicker, higher in net:gross, and more channelized. Downdip, the turbidite reservoirs are thinner bedded, finer grained and with depositional architectures that are characterized by stacked lobes and minor channels controlled by accommodation space and salt movement. In updip fields, such as Nelson and Forties, production is mature. High-quality reservoir channel sands are mostly drained. Recovery factors of 60–62% are achievable by application of water injection and 4D seismic technologies. The remaining challenge in these reservoirs is to (1) find by-passed oil in the channel facies and (2) to identify/model oil remaining in non-channelized facies, such as channel margin and interchannel facies. Portions of the channelized reservoirs have not been swept because of non-uniform water ascent and breakthrough or shale barriers. Non-channelized reservoirs have not been swept because their sands are thin bedded, interbedded with shales and of lower reservoir quality. Remaining oil zones are not correlatable between existing wells, emphasizing the uncertainties of lateral heterogeneities away from the wellbore and the importance of static reservoir modelling techniques to properly model, identify and plan infill targets with multiple realizations. Higher recovery factors (possibly as high as 70%) may be achievable with higher resolution seismic interpretations and reservoir models, application of enhanced oil recovery and sharpshooter drilling techniques and improved water management. In downdip fields, such as Scoter, Merganser, Pierce and Guillemot A, production is not as mature and wells are not as abundant. Consequently, development planning is more dependent on high-quality static and dynamic reservoir models to predict the interwell reservoir character, volumetrics and performance. In general, turbidite reservoir sandstones are thinner and finer grained. The thickest sands may be more correlatable as lobes/sheets. Permeability is lower than in updip reservoirs of equivalent porosity (tens of mD as opposed to hundreds or thousands of mD), probably due to reductions in mean grain size and textural maturity and a corresponding increase in detrital clay matrix. The greatest challenges lie in modelling lateral changes in net:gross, bed thickness, facies (especially shale bed architecture) and cementation. Where depositional slopes were oversteepened by the growth of salt diapirs, slumps and slides introduce lateral heterogeneities and reduce predictability in the reservoir section. Multiple faults radiate from such salt diapirs and may compartmentalize the reservoir. These effects may be mitigated by the construction of robust conceptual models of reservoir accumulation and architecture, supported by relevant field analogues and detailed biostratigraphy which may delineate multiple widespread marker horizons. For liquid hydrocarbons, recovery factors are typically 40–45%. Gas recovery factors are projected to be 60–65%.

Deep-water leveed-channel complexes of the Cerro Toro Formation, Upper Cretaceous, southern Chile

The Cerro Toro Formation in the Torres del Paine National Park, southern Chile, contains a series of deep-water channel complexes deposited in an elongate Andean foreland basin during the Late Cretaceous. This stratigraphic interval represents an essentially continuous depositional record of migrating, leveed-channel complexes. Collectively, the channel-fill units in the study area form a belt approximately 5 km (3 mi) wide and several hundred meters thick. Within the study area, four sets of channel complexes are identified. This paper focuses on the best exposed of these channel-complex sets (channel-complex set 3). The channels are filled by bedded conglomerate and amalgamated sandstones interpreted to represent the deposits of high-concentration turbidity currents and debris flows. Large-scale cross-beds in some of the conglomerates indicate significant bed-load transport of gravel- and cobble-forming bars in the channels. Channel axis to margin facies changes between clast-supported conglomerate and either (1) thick-bedded sandstone or (2) matrix-supported conglomerate are observed. Channel-fill facies lie on erosional surfaces that cut into adjacent interchannel facies. Beds thin and onlap these surfaces toward the channel margins. Shale or siltstone drapes of the channel cuts are uncommon and laterally discontinuous. Bed continuity between channel and adjacent, interchannel facies is not observed. The interchannel strata are interpreted to represent levee successions that bound the channels. Stratigraphy in the levee units is defined to include (1) basal, sandy lobe deposits comprised of medium- to thick-bedded turbidites and (2) overbank facies consisting primarily of packages of fining- and thinning-upward, fine-grained, thin-bedded turbidites. This vertical succession is transitional. Distal levee facies include mudstones with thin-bedded, laterally continuous sandstones. Proximal levee facies include mudstones with both thin- and thick-bedded sandstones; however, the thick-bedded sandstones have lower lateral continuity. The proximal levee facies have a higher sandstone percentage than the distal levee, but also have greater depositional and postdepositional complexity, with sand-filled crevasses, erosional truncation, and slumped beds. Field observations suggest that these leveed channels formed in stages that are represented by depositional and/or erosional events. In chronological order, these are (1) an initial stage of relatively unconfined, sand-rich deposition; (2) aggradation of a mud-rich, confining levee system resulting from overbank deposition as turbidity flows bypass the area; (3) erosion as the channel becomes entrenched or as the channel migrates; and (4) filling of the channel-margin relief by onlap of channel-fill sediments. These stages appear to have repeated several times during the formation of a series of channel complexes. In these ways, the Cerro Toro Formation appears analogous to leveed-channel systems observed in late Pleistocene submarine fans and subsurface examples.

Evolution of an ancient coastal plain: palaeosols, interfluves and alluvial architecture in a sequence stratigraphic framework, Cenomanian Dunvegan Formation, NE British Columbia, Canada

To date, discussion of changes in alluvial style and in the character of palaeosols in relation to changes in accommodation and sediment supply on floodplains has primarily been from a conceptual standpoint: few case studies are available against which to test ideas. One hundred and thirty metres of non‐marine strata of the Dunvegan Formation were examined in 14 closely spaced sections in the canyon of the Kiskatinaw River, NE British Columbia, Canada. This site was located about 120 km inland from the transgressive limit of the contemporary marine shoreline and represents almost exclusively freshwater environments. Fluvial channels in the Kiskatinaw River section are of two types. Small, single‐storey, very fine‐ to fine‐grained sandstone ribbons with W/T ratios <30, encased in fine‐grained floodplain sediments are interpreted as anastomosed channels. Fine‐ to medium‐grained, laterally accreted point‐bar deposits forming multistorey sand bodies with individual W/T ratios >30 are interpreted as the deposits of meandering rivers filling incised valleys. Interchannel facies include the deposits of crevasse channels and splays, lakes, floodplains and palaeosols. Floodplain palaeosols consist of laterally heterogeneous, simple palaeosol profiles and pedocomplexes similar to modern Entisols, Inceptisols and hydromorphic soils. Interfluve, sequence‐bounding palaeosols adjacent to incised valleys are laterally continuous, up to 3 m thick and can be reliably identified using a combination of (1) stratigraphic position; (2) field observations, such as thickness, structure, colour, degree of rooting; and (3) micromorphological features, such as evidence of bioturbation, clay coatings, ferruginous features and sphaerosiderite. Interfluve palaeosols are similar to modern Alfisols and Ultisols. Correlation of the local stratigraphic succession with the regional sequence stratigraphic framework, based on 2340 well logs and 60 outcrop sections, shows that the vertical changes in coastal plain character (more coals and lakes vs. more pedogenesis) can be related to relatively high‐frequency base level cycles (eustatic?) that are expressed as transgressive–regressive marine cycles in downdip areas. Regional isopach maps show that these cycles were progressively overprinted and modified by an increasing rate of tectonic subsidence in the north and west. The character of palaeosols developed on aggrading floodplains primarily reflects local sediment supply and drainage. In contrast, well‐developed interfluve palaeosols record pedogenesis during periods of reduced or negative accommodation (base level fall). Vertical changes in floodplain palaeoenvironments and palaeosol types reflect changes in accommodation rate. The detailed micromorphological analysis of interfluve palaeosols represents a powerful application of an under‐used technique for the recognition of key surfaces in the geological record. This has broad implications for non‐marine sequence stratigraphy.

SEISMIC STRATIGRAPHIC EVALUATION OF A NEOCOMIAN SUBMARINE FAN SYSTEM, BROWSE BASIN, NORTH WEST SHELF

A possible submarine fan system of Valanginian age occurs in the south of the western half of Permit WA-212-P in the Browse Basin. Seismic mapping and interpretation have allowed the recognition of five seismic facies which are considered representative of this fan system.The five seismic facies are the upper-middle fan braided channel facies, the upper-middle fan braided interchannel facies, the lower fan channel facies, the lower fan sheet facies, and the lower fan lobe fringe facies. The reflections of the upper-middle braided channel fan facies are discontinuous, disrupted, convex up, low amplitude and high frequency. The interchannel facies has reflections that are concave up, continuous, low frequency and moderate to high amplitude. The lower fan channel facies are recognised by convex up, discontinuous, high frequency and low amplitude reflections. The lower fan sheet facies is noted by mounded configurations with continuous, moderate to high amplitude, moderate frequency reflections. The lower fan lobe fringe facies reflections are flat, often shingled reflections with moderate discontinuity, moderate to high amplitude and low to moderate frequency.Since no wells penetrate the submarine fan, the interpretation is based on seismic reflection configurations which are considered typical of submarine fan segments. The interpreted ancient submarine fan occurs on the basin floor adjacent to a probable ramp type margin, and manifests shape and setting consistent with known submarine fans, such as the Eocene Frigg Fan of the North Sea, and the Lower Cretaceous Barrow Group turbidites in the Carnarvon Basin.Seismic facies mapping, in conjunction with sequence stratigraphy concepts, is particularly useful in areas such as the Browse Basin where considerable marine shale sections exist with little structure, and sequences with reservoir potential continue to be a problem to locate. For instance, in Caswell-1, a well drilled in 1977 immediately north of the permit area, 200 barrels of oil flowed from thin sands within a shale sequence of Albian age. Results of this study indicate that local seismic reflection signatures may be indicative of potential sandstone reservoirs in the vicinity of the study area.

Delineation of a Deep-Water Channelized Fan Interval Using 3-D Horizon Slice, Offshore Texas: ABSTRACT

The High Island A-467 field is located in the Pliocene producing trend, 90 mi southeast of Galveston, Texas. Gas is produced from 10 reservoir zones ranging in depth from {minus}6,500 to {minus}10,000 ft. Reservoir sands were deposited in upper slope submarine fan complexes. The late Pliocene (Globoquadrina altispira) I-2 producing zone is a 200-ft-thick interval containing multiple reservoirs formed from deposition of sand in several channel systems and their associated deposits. Delineation of the I-2 reservoir system has been possible with the combination of a three-dimensional seismic volume, well log interpretation, and production or test data. Construction of an amplitude strength (bright spot) map on the I-2 seismic event reveals trends in gas-charged areas that can be linked to reservoir geometry through depositional models and production behavior. Areas in the reservoir system containing gas-filled channels are revealed by elongate and parallel amplitude trends which, using well logs and sidewall core samples, are shown to contain fine-grained fining-upward cycles that pinch out laterally. These channelized fills, which are 25-100 ft thick occupy staggered stratigraphic positions, suggesting a degree of compensation during sedimentation. Areas of interchannel deposition, where gas charged, lack distinctive amplitude trends but are characterized by increases in amplitude strengthmore » over broad areas. Wells in these areas contain thinner and more heterogeneous gas reservoirs. Producing characteristics between the channel and interchannel facies differ in decline history, drive mechanism, and gas-oil ratios, necessitating this type of reservoir delineation for efficient exploitation of reserves.« less

Depositional Systems and Oil Reservoirs in Spraberry Formation (Permian), Midland Basin, Texas: ABSTRACT

Terrigenous clastic submarine-fan facies comprise the upper and lower parts of the Spraberry Formation (Permian, Leonardian) of west Texas. The Jo Mill submarine-fan system makes up the lower Spraberry. The upper Spraberry comprises the Driver and the overlying Floyd submarine-fan systems. The Midland basin plain system, composed mainly of shales and carbonates with thinner, interbedded sandstones, makes up the middle Spraberry and vertically separates the Jo Mill and Driver fans. Sand-rich inner fan facies of all three fan systems extend 50 mi into the Midland basin from the northern shelf edge. The abrupt transition from inner to midfan facies coincides with the underlying Horseshoe atoll, suggesting this bathymetrically positive feature influenced sedimentation patterns in younger sediments. Midfan to outer fan facies extend downdip from the subjacent atoll 100 mi farther into the basin. Sand contents decrease and interbedded mudstones thicken basinward. Recovery efficiencies are strongly related to submarine-fan facies. Recoveries in inner fan, incised-channel reservoirs (24% in Jo Mill field) are higher than in midfan and outer fan reservoirs (5% in the Spraberry trend to 15% in Benedum field). These more distal reservoirs consist of anastomosing to meandering channel-fill and interchannel facies associations. Stacking of channels through time resulted inmore » dipelongate depositional axes in which wells have produced from two to as much as six times more oil than wells tapping interaxial areas. Pronounced stratigraphic heterogeneity and current well completion practices result in partly drained reservoir compartments, providing abundant opportunities for additional oil recovery.« less

Depositional Environments in an Alluvial-Lacustrine System: Molluscan Paleoecology and Lithofacies Relations in Upper Part of Tongue River Member of Fort Union Formation, Powder River Basin, Wyoming: ABSTRACT

The upper part of the Tongue River Member of the Fort Union Formation (Paleocene) in the northern Powder River basin, Wyoming, contains assemblages of excellently preserved nonmarine mollusks which occur in laterally continuous outcrops of diverse lithologic sequences and sedimentary structures. These attributes offer a unique opportunity for interdisciplinary interpretation of depositional environments based on molluscan paleoecology and lithofacies relations. Taphonomic histories of mollusk assemblages as reflected by molluscan biofabric (size, End_Page 478------------------------------ shape, orientation, and distribution of faunal elements), and the taxonomic composition, diversity, and abundance representation of species in assemblages are of particular importance in interpretations of paleoecology and depositional environments. Three facies are recognized vertically within an alluvial-lacustrine system. The interfluvial lake and lake splay facies is characterized by sequences of coarsening-upward detritus, abundant continuous limestone beds, and few beds of discontinuous coal and continuous carbonaceous shale. Limestones, contain two lacustrine mollusk assemblages: a locally reworked assemblage dominated by the bivalve Plesielliptio (two species), and the gastropods Viviparus, Lioplacodes (three species), and Clenchiella; and a quiet-water assemblage dominated by sphaeriid bivalves. This facies reflects development of numerous lakes bordered by well-drained backswamps in interfluvial flood basins. Lakes were repeated infilled by carbonate mud, splay detritus, and backswamp deposits. The interfluvial crevasse splay-crevasse channel facies is characterized by sequences of coarsening-upward detritus and few discontinuous limestone beds, separated vertically by thick, continuous coal and carbonaceous shale beds. This facies includes small crevasse channel sandstones which scour into splay sandstones. Biofabric of lacustrine mollusk assemblages, which are identical in composition (but with dwarfed species of Plesielliptio) to locally reworked lacustrine assemblages of the interfluvial lake and lake splay facies, reflects deterioration of lakes through active infilling by crevasses. The fluvial channel and interchannel facies is typified by thick channel sandstones laterally separated by sequences of coarsening-upward detritus, overbank sediments, and rare limestones. This facies includes thick, continuous coal and carbonaceous shale beds. Muddy-substrate flood basin lakes are characterized by an untransported lacustrine mollusk assemblage differing from those of the interfluvial lake and lake splay facies in both composition and relative abundance of species. Transported mollusk assemblages dominated by the gastropod Hydrobia eulimoides occur in crevasse sandstones. Relative to northerly flowing major channels, proximal and distal parts of splay deposits can be differentiated by their mollusk assemblage composition. The fluvial channel and interchannel facies re lects deposition on flood basins that were formerly occupied by lake, crevasse, and backswamp deposits. Thick, continuous coal beds reflect the spread of backswamps from interchannel depressions to abandoned major channel ridges. Cessation of fluvial channel and interchannel sedimentation was marked by widespread lacustrine deposition. The vertical sequence of facies just described also reflects the areal distribution of deposits of major channels that pass laterally into overbank and crevasse splay channel areas, which in turn merge into large and small lakes. Alluvial-lacustrine deposition in the upper part of the Tongue River Member is similar to that of anastomosed reach of the Saskatchewan River, Canada, as reported in a 1980 study by Smith and Putnam. End_of_Article - Last_Page 479------------

Facies and Depositional Environments of Energy Shale Member (Carbondale Formation, Pennsylvanian), Southwestern Jefferson County, Illinois: ABSTRACT

The Energy Shale directly overlies the Herrin (No. 6) Coal Member in southwestern Jefferson County. Five facies of the Energy are recognized in the study area. The depositional environment is interpreted as a large quiet-water bay into which periodic influxes of coarse-grained sediments from the nearby Walshville channel were deposited as crevasse splays. The bay-fill deposits include a nonmarine and a brackish-marine facies; the latter has higher sulfur and boron contents and a sparse marine fauna. Both bay-fill facies are faintly laminated gray shales, and both grade laterally into and underlie deposits of the distal portion of crevasse splays. The distal splay facies is dominantly siltstone with lenticular bedding. The proximal splay facies grade laterally into and are interbedded with the distal splay deposits, and are divided into a channel facies (characteristically a well-sorted sandstone that contains microcross-bedding, clay drapes, contorted bedding, and a shale clast lag-deposit) and an interchannel facies (characterized by massive and flaser-bedded sandstones). Sulfur and boron content of the proximal and distal splay deposits is considerably less than that of the brackish-marine bay deposits, suggesting a nonmarine origin. Energy Shale facies have a direct influence on the sulfur content of the underlying Herrin (No. 6) Coal. In areas where thick (> 20 ft, 6 m) nonmarine bay-fill deposits overlie the coal, the sulfur content of the coal is less than 1%. Where the coal is overlain by thick proximal splay deposits, the sulfur content is 2 to 3%. This increase in sulfur content is attributed to downward percolation of sulfate-rich marine waters of a later transgression through the permeable sandstone. Where the coal is overlain by thin brackish-marine Energy or by the Anna Shale, the sulfur content averages 4 to 5%. End_of_Article - Last_Page 1454------------

Slope and Deep-Sea Fan Facies of Miocene Castaic Formation and Lower Part of Ridge Route Formation, Ridge Basin, Southern California: ABSTRACT

The late Miocene marine Castaic Formation in Ridge basin is over 2,000 m (6,600 ft) thick and consists mostly of slope and deep-sea fan facies. The Castaic Formation is vertically transitional into the overlying Marple Canyon Sandstone Member of the Ridge Route Formation and laterally interfingers with the Violin Breccia to the southwest. The slope facies consists of poorly bedded mudstone interbedded with sandstone, conglomerate, and coquina deposits interpreted as turbidite-filled slope channels. The slope facies follows the northwest trend of the basin and occurs on the northeast, north, and southwest sides of the basin. The slope channels have laterally adjacent levee deposits. Paleocurrents in the channels are to the west-northwest and southwest-southeast, whereas pa eocurrents in the levee deposits are to the northwest-southeast. Large slide blocks, slump-folded strata, and breccia beds are common in the slope facies. Deep-sea fan deposits consist of inner and middle fan channel and interchannel facies and outer fan depositional-lobe facies. They are confined to the center of the basin, interfinger into slope facies to the southwest and northeast, and are overlain by nonmarine fan-delta complexes to the north. The channels contain thick sandstone deposits that thin and fine upward and are laterally discontinuous, whereas the adjacent interchannel deposits consist of thin-bedded sandstone and mudstone sequences which form inclined wedges of highly slump-folded strata. Depositional-lobe facies thicken and coarsen upward and consist of interbedded sandstone and mudstone which form laterally continuous deposits with minor channeling and slump folding. Paleocurrents in these deposits are to the south-so theast and suggest sediment transport down the axis of the basin from the north-northeast. Ridge basin was a relatively shallow-marine trough about 6 km (4 mi) wide and 10 to 20 km (6 to 12 mi) long. The deep end of the basin was to the southwest and connected to the Ventura basin across the San Gabriel fault. Typical deep-sea fans did not develop in Ridge basin during Castaic Formation time; instead extensive slope deposits formed along the margins of the basin and thick but narrowly confined turbidite-filled channels and depositional lobes filled the valley or trough of this basin. End_of_Article - Last_Page 504------------

Paleoenvironmental Control of Biogenic Structures in Upper Devonian Prodeltaic Turbidite Deposit: ABSTRACT

The Rock Stream Formation near Ithaca, New York, is a proximal, submarine fan-like deposit of an epicratonic sea. Turbidites and interbedded shale were deposited in alternating channel and interchannel facies. This lithology is in sharp contact with overlying mudstones which were probably deposited on a progradational slope. The complex environmental parameters which affect the distribution of trace-making organisms is shown by their ichnologic distribution. Three associations occur within the submarine fan. (1) The Paleodictyon association consists of five ichnogenera representing pascichnia. These are followed stratigraphically by (2) the Arenicolites association consisting of 12 ichnogenera representing domichnia and fodinichnia. Two repichnia compose (3) the Pteridichnites association. This last association is ubiquitous to the study section. Food resources significantly influenced behavior as the population shows a trophic shift within a lithologically consistent section, from grazing (like Nereites) to the endobenthic feeding and dwelling behavior of a shallow-water assemblage. Within the Arenicolit s association, substrate texture and cohesion differentially influence the distribution of suspension-feeders and deposit-feeders through a trophically consistent assemblage. Multiple ichnogenera among any one behavioral class rarely occur in the same bed. Ecologic competition affects the distribution of individual phylotaxa within a behavioral class. Ecologic competition may have depended mostly on spot concentration at the time of substrate availability. On muddy substrates which may vary widely in cohesiveness, trophic group ammensalism allows fodinichnia to inherit a similar lithology from domichnia. The complexity of ichnogeneric distribution is produced by ichnotaxa ambiguities as well as ecological controls. End_of_Article - Last_Page 694------------